1. Field of the Invention
The invention relates to a method for controlling air volume output by a motor.
2. Description of the Related Art
In an indoor ventilation duct of a household air-conditioner, static pressure often changes because of dust deposition in a duct or blockage of a filter. The static pressure is often higher than the standard static pressure for a nominal system of a manufacturer laboratory due to different installations of ducts. Constant air volume control can provide constant air volume for users under such cases, so as to maintain the comfortable ventilating, cooling or heating effect under broad static pressure conditions.
To realize the constant air volume control, an air volume meter is installed, which, however, increases the cost and the potential risk due to failure of the air volume meter. Currently, air conditioner manufactures mostly adopt a method for controlling air volume provided to remain constant without an air volume meter.
In addition, in some technical schemes, rotational speed is adjusted by monitoring the changes of static pressure to obtain constant air volume. A typical method for determination of the air volume is to directly measure the external static pressure, which requires that the relationship between the static pressure and air volume is measured in advance, then the torque of a motor is calculated under the static pressure corresponding to the specified air volume, and speed adjustment is carried out by monitoring the changes of static pressure. Some calculation formulas involve logarithmic computation or high-order polynomials, and this requires that a microprocessor control unit (MCU) for a motor controller has stronger calculating ability, thus the cost is further improved.
As an improvement, a method for controlling constant air volume for a motor employs a first-order or second-order function to describe the system and does not require to measure a real-time static pressure; thereby simplifying the structure of the fan system and the mathematical model, furthermore, the requirement of the computing capacity of an MCU (Micro Controller Unit) for the motor controller is not high, thereby lowering the production cost. However, the method has the following defects: 1) a control accuracy of the method is relatively poor in some situations; 2) the method lacks a process for correct an individual air volume, when the overall test result is good, but accuracy problems exist in some of the operating positions. The method cannot employ compensating means to improve the accuracy of these operating positions on the premise of no affecting other operating positions.